1. Field of the Invention
This invention generally relates to an image processing system for processing image data and coded image data (hereunder sometimes referred to as image code data or simply as code data) and to an image communication system such as a facsimile system for receiving image code data and reproducing an image on a sheet of recording paper. More particularly, this invention relates to an image processing system for carrying out various functions, which are necessary for a facsimile system or the like, such as compression of image data, expansion of image code data, conversion (namely, enlargement or reduction) of an image represented by image data and conversion of a code representing image data to another type of code representing the image data. Further, this invention particularly relates to an image communication system for following a communication procedure to simultaneously transmit image code data to a plurality of image-receiving terminals by using a plurality of circuits or lines, for appreciating the receiving capability of each image-receiving terminal and for performing a code conversion of image code data according to the appreciated receiving capability of each image-receiving terminal.
2. Description of the Related Art
The above described image processing system is needed in an image communication system such as a facsimile system and a picture file system.
FIG. 1 illustrates an example of a conventional facsimile system. This conventional facsimile system is provided with two compression/expansion devices for performing expansion of received image code data and compression of image data (namely, a first compression/expansion device 8001 and a second compression/expansion device 8002) and an image conversion device 8003 for performing enlargement/reduction (namely, image conversion) of an image represented by image data. These devices interface to both of a system bus 8005 and an image bus 8006.
The received code data is first demodulated by a modem 8007. Then the demodulated code data is buffered, namely, stored in a compression data memory 8009 on (or connected to) the system bus 8005. Subsequently, the buffered code data is decoded by, for example, the first compression/expansion device (namely, the compression/expansion device #1) 8001. Thereafter, restored image data is stored in an image page memory 8010 on the image bus 8006. Incidentally, a random access memory (RAM) 8016 is used as a reference line memory.
When image data of one page is restored and parameters such as the number of lines of an image represented by the restored image data are obtained, a ratio of enlargement or reduction of this image (hereunder sometimes referred to as a scaling ratio of image data) is determined and then the image conversion device 8003 is informed of the determined scaling ratio. Thereafter, enlargement or reduction of the image data stored in the image page memory 8010 is performed by the image conversion device 8003. Upon completion of the conversion (namely the expansion or reduction), the converted image data is transferred through a recording image processing unit 8011 to a printer 8012 whereupon the transferred image data is printed on a sheet of recording paper.
In case that a request to read an original page of a draft to be transmitted occurs during a receiving operation as above described, the page to be transmitted is first scanned by an image scanner 8014. Then output signals of the image scanner 8014 is processed by a read-image processing unit 8015 to generate transmitting-draft image data representing an image of the original page of the draft. Subsequently, the transmitting-draft image data is sent through the RAM (hereunder sometimes referred to as the line buffer) 8016 on the image bus 8006 to the second compression/expansion device (namely, the compression/expansion device #2) 8002 whereupon the sent image data is coded. Code data obtained by the device 8002 is stored in a compression data memory 8009. Additionally, the RAM 8016 is used as a coding line memory and a reference line memory.
Such a conventional compression/expansion device has a structure as illustrated in FIG. 2. In this figure, reference numeral 8050 representing an image bus unit for interfacing with the image bus; and 8051 a system bus unit for interfacing with the system bus. Image data and code data are inputted and outputted through these bus units 8050 and 8051 as 16-bit-parallel word data and 8-bit-parallel word data, respectively.
In this compression/expansion device, composing elements for performing a coding of image data are a changing-pixel-of-reference-line detection portion 8052 for detecting an address of a changing pixel (namely, a changing pel) of a reference line, a changing-pixel-of-coded-line detection portion 8053 for detecting an address of a changing pixel of a coding line, a coding mode judgement portion 8054 for judging which of vertical, horizontal and pass modes a coding mode is, by using information on the address of the changing-pixel, a coding-table retrieval portion 8055 for effecting code assignment on the basis of a result of the judgement made by the coding mode judgement portion 8054 and a coding table read-only memory (ROM) (hereunder sometimes referred to simply as a coding ROM) 8056.
Further, composing elements for performing a decoding of code data are a decoding-table retrieval portion 8058 for analysis of code data, a decoding table ROM (hereunder sometimes referred to simply as a decoding ROM) 8059, an a0-address calculation portion 8060 for calculating the address of a starting point of a decoding line or the address of a reference changing-pixel a0 (see CCITT (Consultative Committee in International Telegraphy and Telephony) Recommendation T. 4) and an image-data drawing portion 8061 for drawing an image represented by image data corresponding to a decoding line. Incidentally, reference numeral 8062 designates a control unit for monitoring the state of the compression/expansion device and controlling the operation thereof.
In case of the conventional compression/expansion device with the above described configuration, when performing a compression operation, the following sequence of operations are effected serially. Namely, image data is inputted thereto in word units and then the address of a changing pixel is detected and coded. Subsequently, code data is outputted therefrom. Therefore, a time required for a compression operation (hereunder sometimes referred to as a compression processing time) is given by the following equation: EQU (A compression processing time)=(Image data input time)+(Coding processing time)+(Code data output time) (1)
where the image data input time is a time required for inputting image data, and the coding processing time is a time required for completing a coding operation, and the code data output time is a time required for outputting generated code data.
The coding line memory and the reference line memory are provided in an external memory (namely, RAM 8016 of FIG. 1) on the image bus. However, an access time for the image bus (hereunder sometimes referred to as a bus access time) is rather long. Further, the lower limit of the time indicated by the second term of the right-hand side (namely, the coding processing time) of the equation (1) depends on this bus access time. Therefore, there is a limitation in speeding-up of a compression operation (and thus of the entire processing of data by the facsimile system).
Especially, in case where a plurality of compression/expansion devices and an image conversion device are provided on or connected to a common bus just as in case of the facsimile system of FIG. 1, a burden on the common bus becomes large. This results in increasing the bus access time. Consequently, the compression processing time becomes noticeably increased due to the increase in the bus access time.
In case of processing image data representing a coarse image, the periods of time respectively indicated by the second and third terms of the right-hand side of the equation (1) are rather shorter than the period of time indicated by the first term of the right-hand side thereof. Thus the compression processing time is substantially dependent only on the image data input time. In contrast with this, in case of processing image data representing a fine image, the coding processing time indicated by the second term of the right-hand side of the equation (1) is increased in comparison with that of the former case (namely, the case of processing image data representing a coarse image). Moreover, in the latter case (namely, the case of processing image data representing a fine image), generated code data increases compared with code data of the former case. Thus the code data output time indicated by the third term of the right-hand side of the equation (1) is increased in comparison with that of the former case. Consequently, the total processing time (namely, the compression processing time) becomes large. Additionally, the total processing time changes very widely according to the contents of image data to be processed.
The same applies to a case of performing an expansion operation.
As is apparent from the foregoing description of an operation of the facsimile system of FIG. 1, when an image conversion of restored image data is needed, the image conversion cannot be commenced until all image data representing an image of one page is restored, because of the necessity of obtaining parameters required to determine a scaling ratio (namely, an enlargement or reduction ratio). Consequently, a bulk memory (namely, the image page memory 8010 of FIG. 1) being capable of storing restored image data representing an image of one page becomes necessary.
Further, the image conversion device is independent of the compression/expansion devices. Therefore, when an image conversion and a compression operation (or an expansion operation) are performed serially, an access to an external bus is necessary for the image conversion. This is also a limitation on speeding-up of the processing.
Next, drawbacks of the image communication system as above described (namely, the image communication system (e.g., a facsimile system) for receiving image code data and reproducing an image on a sheet of recording paper) will be described hereinbelow.
When recording paper corresponding to a regular paper size is used in such an image communication system, it becomes necessary for recording a received image in a reproduction area on recording paper with an appropriate size to perform enlargement/reduction processing of the received image before the recording thereof. For instance, a conventional facsimile system employing a laser beam printer (hereunder abbreviated as LBP) as an image recording means generally uses recording paper of regular paper sizes and thus is adapted to perform the enlargement/reduction processing.
FIG. 3 illustrates the configuration of such a conventional facsimile system. In this figure, reference numeral 5050 denotes a read-image processing unit; 5051 an LBP recording device; 5052 a compression/expansion device; 5053 an image conversion device; 5054 an image page memory; 5055 a compression data memory; 5056 a microprocessor unit (MPU) having a direct-memory-access (DMA) controller; 5057 RAM/ROM; 5059 a control unit having MPU 5056 and RAM/ROM 5057; 5060 a modem; and 5061 a network control unit (NCU).
Hereinafter, a receiving operation of the conventional facsimile system of FIG. 3 will be described by referring to a flowchart of a program shown in FIG. 4.
Under the control of the control unit 5059, image code data received in what is called a message sending procedure (corresponding to Phase C (namely, a phase of sending fax signals for the page being copied) of the standard facsimile protocol or procedure (see CCITT Recommendation T.30)) is demodulated by the modem 5060. Then, the demodulated data are serially stored in the compression data memory 5055 in step 5300 of FIG. 4. Thereafter, the code data stored in the compression data memory 5055 is read into the compression/expansion device 5052 whereupon the read code data is decoded. Subsequently, in step 5301, data obtained as the result of the decoding is stored in the image page memory 5054 as image data (namely, raw data). The above-mentioned processing of these steps is performed on each line. Incidentally, the image page memory 5054 has a memory capacity sufficient to store image data representing an image of one page. Upon completion of reception of the code data corresponding to an image of one page in step 5302, the program exits therefrom to YES-branch and advances to step 5303 whereupon the device continues to effect a decoding of the code data which has not been decoded. Upon completion of the decoding of the code data corresponding to an image of one page in step 5304, namely, when the program exits therefrom to YES-branch, parameters such as the number of lines of one page and the numbers of continuous white lines at the top and bottom of the page are obtained. Thus the control unit 5059 can determine a scaling ratio (namely, an enlargement ratio or a reduction ratio) on the basis of the parameters. In case where enlargement or reduction of an image represented by the image data, the control unit 5059 sets the determined scaling ratio in the image conversion device 5053 and causes the image conversion device 5053 to perform enlargement or reduction of the image represented by the image data stored in the image page memory 5054. Then, in step 5305, the control unit causes the LBP recording device to record the processed image data. Thereafter, when it is found in step 5306 that the final line of the enlarged or reduced image represented by the processed image data is recorded, the program exits therefrom to YES-branch and thus the processing of image data corresponding to the image of one page is completed.
This conventional image communication system, however, has drawbacks in that a mass image page memory is necessary and moreover, at the time of reception, this memory cannot be used for another purpose and thus the communication is uneconomical.
Next, drawbacks of the other image communication system as above described (namely, the image communication system for following a communication procedure to simultaneously transmit image code data to a plurality of image-receiving terminals by using a plurality of circuits or lines, for appreciating the receiving capability of each image-receiving terminal and for performing a code conversion of image code data according to the appreciated receiving capability of each image-receiving terminal) will be described hereinbelow.
An example of such a conventional image communication system is what is called a facsimile (Fax) mail system. FIG. 5 shows the configuration of a conventional facsimile mail system. This conventional facsimile mail system is adapted to receive facsimile data (namely, image code data) from a Group 4 transmitting terminal through an integrated services digital network (ISDN) circuit and to simultaneously transmit the received data to three Group 3 facsimile receiving terminals at the most by using Group 3 circuits #1 to #3. As shown in this figure, in this system, an ISDN interface circuit 5550, a memory 5551, a control unit 5552 and blocks 5553 respectively corresponding to the Group 3 circuits (thus the number of blocks 5553 is equal to that of the Group 3 circuits connected to this system) are connected to a system bus 5570.
As shown in this figure, each of the blocks (hereunder sometimes referred as Group 3 circuit corresponding blocks) 5553 contains a modem 5554, an NCU (namely, a network control unit) 5555, a compression/expansion device 5556 and an enlargement/reduction device 5557. Further, the compression/expansion device 5556, the enlargement/reduction device 5557 and an (external) memory 5558 are connected to an image bus 5559. The control unit 5552 is used to follow facsimile procedures and to control an operation of each of the remaining portions of this system, as well as data transmission. Furthermore, the control unit 5552 is provided with a microprocessor unit/DMA controller unit (MPU/DMAC) 5560 and a memory (RAM/ROM) 5561.
Data received from a Group 4 facsimile transmitting terminal is sent through the ISDN interface circuit 5550 to the memory 5551 and is stored in this memory. Upon completion of receiving this data, the control unit 5552 calls N Group 3 facsimile receiving terminals through the Group 3 corresponding blocks 5553, which biuniquely correspond to the Group 3 circuits #1 to #N. Subsequently, the control unit 5552 appreciates the receiving ability or capability (e.g., an employed coding method and paper size of reception recording paper) of each of the called facsimile receiving terminals in the course of the facsimile procedure and causes each of the corresponding blocks 5553 to perform code conversion (including paper size conversion and image conversion) of data stored in the memory 5551 to data meeting the receiving ability of the corresponding facsimile receiving terminals. Thereafter, the control unit 5552 transmits the converted data to the facsimile receiving terminals.
FIG. 6 illustrates an example of a communication sequence in case of this conventional facsimile mail system. As is seen from this figure, the receiving ability of the Group 3 facsimile receiving terminal connected to each Group 3 circuit is appreciated from a digital identification signal (DIS) received in Phase B of the facsimile procedure. At that time, code conversion processing (namely, decoding, enlargement/reduction processing and coding of received data) is started. Thereafter, the code conversion processing is finished before the system enters Phase C of the facsimile procedure. Incidentally, the code conversion processing may be performed in Phase C of the facsimile procedure.
Such a conventional facsimile mail system, however, has drawbacks in that the system should be provided with expensive Group 3 circuit corresponding blocks, the number of which is equal to that N of Group 3 circuits or lines respectively transmitting data to be simultaneously processed, and thus, in case where the number of the Group 3 circuits accommodated by or connected to the system is large, the structure of the system becomes extremely complex and the system becomes very costly.
The background causing such drawbacks is the fact that the code conversion rate of the Group 3 circuit corresponding block 5553 is small. Namely, in the Group 3 circuit corresponding block 5553, the received data is sent to the compression/expansion device 5556 to decode the data and then, the image data representing a restored image obtained as a result of the decoding is once stored in the external memory 5558. Thereafter, enlargement/reduction processing (namely, an image conversion) is performed on the image data, which is stored in the memory 5558, by the enlargement/reduction device 5557. Subsequently, image data obtained as a result of effecting the enlargement/reduction processing is sent from the memory 5558 to the compression/expansion device 5556 to perform a coding of the sent image data. Then, the coded data is sent back to the memory 5551. As described hereinabove, the code conversion is carried out by performing such a serial processing sequence. Further, image data of a reference line to be used at the time of effecting a coding or a decoding is stored in the external memory 5558. Thus, the number of times of accessing the image bus 5559 in relation to the code conversion processing is very large. In other words, access time related to the code conversion processing is long. This is also a limitation on a speeding-up of the processing.
The present invention is accomplished to eliminate the above-mentioned drawbacks of the conventional systems.
It is, accordingly, an object of the present invention to provide an image processing system which can perform operations necessary in a facsimile system (namely, a compression operation, an expansion operation, an image conversion operation and a code conversion operation).
Further, it is another object of the present invention to provide an image communication system which does not require a mass image page memory even when recording a received image on recording paper of a regular paper size at a high speed by using LBP or the like.
Moreover, it is a further object of the present invention to reduce the capacity of a memory for storing image code data and utilize this memory effectively.
Furthermore, it is still another object of the present invention to provide a facsimile mail system which has a simple and inexpensive structure being capable of meeting cases where the the number N of Group 3 circuits respectively transmitting data to be simultaneously processed is large.
Additionally, it is yet another facsimile mail system which can easily cope with increase in lines or circuits and restrain an associated rise in cost.